1. Field of the Invention
This invention relates to cyclic pyrophosphate derivatives, their process of preparation, a dental filling material composed of the same, and a dental filling technique making use of this material.
2. Description of the Prior Art
Many kinds of dental cements have been applied as dental filling materials. Recently, some monomers of methacrylate, as the resin-based filling material, have been given attention as well. One of the well-known monomers is a compound of the following formula (glycidyl methacrylate derivative of bisphenol A; Bis-GMA): ##STR2## which is disclosed in U.S. Pat. Nos. 3,066,112 and 3,179,623. To this monomer are added the proper reactive diluents, such as methyl methacrylate, ethyleneglycol dimethacrylate, triethyleneglycol dimethacrylate or tetraethyleneglycol dimethacrylate, making the mixture less viscous and thereby suitable for practical use. For filling cavities of teeth, tert.-amines and peroxides are added to the mixture, which is then cured to serve as an excellent restorative material of higher mechanical properties.
The handling characteristics of this material are not very good, since Bis-GMA is extremely viscous absent a large quantity of diluent and sometimes tends to absorb undesirable amounts of water which causes trouble in that a less cured resin is obtained which has lower mechanical strength. Also, as a fundamental problem, the hardening time between gelatination and complete hardening is too long and patients are greatly discomfited waiting until the resin is completely cured.
Additionally, since the diluents described above are low molecular weight monomers which penetrate into pulpal tissues, they irritate the patient, and it would be desirable to reduce the amount of diluent as much as possible.
A need therefore continues to exist for a resin monomer which overcomes the above-mentioned difficulties and which can be completely polymerized in a short period of time without the necessity of adding low molecular weight diluents.